huawei hspa basic principle

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HSDPA Basic Principle


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Learning Objectives

HSDPA basic principle and feature

HSDPA key technologies

HSDPA physical channels





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Contents

Chapter 1 HSDPA Basic Concepts and Characteristics

Section 2 Key Techniques

Section 3 Physical Channel





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HSDPA Basic Concepts

HSDPA = High Speed Downlink Packet Access Important Features of 3GPP R5 Why HSDPA?

The subscribers request higher speed and better quality data access

Competition challenge from CDMA EV/DO, WiMAX Up to now, the throughput request for downlink is much

more higher than that of uplink The channel configuration of R99 lead a very low

efficiency on the downlink capacity





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HSDPA Characteristics

HSDPA is the solution of WCDMA offering higher speed downlink data services.

Peak data rate in DL: 14.4Mbps (physical layer) Shorter delay Higher efficiency using downlink code and power and bigger

downlink capacity Flexible cell resource allocation More high speed user access

UMTS R99

GSM

HSDPA





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Contents


Chapter 2 Key Techniques

Chapter 3 Physical Channel





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HSDPA Key Techniques- OverviewHSDPA Key Techniques- Overview

AMC Fast SchedulingHARQ (Hybrid ARQ)

16QAMSF16, 2ms and CDM/TDM 3 New Physical Channels

Adaptive Modulation and Coding Hybrid Automatic Repeat Request





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HSDPA Key Techniques

Fast Scheduling(2ms short frame and scheduling)

AMC (support QPSK and 16QAM) HARQ





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Fast Scheduling Basic

If a little part of received 10ms frame (15 slots - R99) can’t be decoded correctly, whole frame will be retransmit 10ms later.

An HSDPA frame is only 2ms(3 slots). If a 2ms frame can’t be decoded correctly, just this 2ms frame need be retransmitted. Other 2ms(up to 6) HARQ process may continue transmitting data, thus radio resource could be used more effectively.

Physical Layer Basic





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Fast SchedulingFast Scheduling

Scheduling Principle: based on channel condition in short period; based on balance between throughout and proportional fair for all users in long period.

Scheduling Principle: based on channel condition in short period; based on balance between throughout and proportional fair for all users in long period.

Some basic scheduler

Round Robin (RR)

Maximum C/I (MAXC/I)

Proportional Fair (PF)

Some basic scheduler

Round Robin (RR)

Maximum C/I (MAXC/I)

Proportional Fair (PF)

By fast scheduling, HSDPA cell can allocate the available HSDPA power resource and code resource among users effectively, to improves the throughout.

Scheduler may works based on CDM

and/or TDM

Channel condition

Amount of data waiting in the queue (delay)

Fairness

Cell throughout, etc

Scheduler may works based on CDM

and/or TDM

Channel condition

Amount of data waiting in the queue (delay)

Fairness

Cell throughout, etc





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Share and Scheduling of Shared Channel

The following fig describes scheduling processing for 4 users.

All codes reserved for HSDPA transmission

2ms





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Fast Scheduling ProcessFast Scheduling Process

•Transmit power for which users

•Channelization code

•Data attributes

•Transmit power for which users

•Channelization code

•Data attributes

Scheduling Algorithm

Available resourceAvailable resource

Required resourceRequired resource

Temporary statisticTemporary statistic

Input:

1. Available resource: power and channelization code

2. Required resource: including users, user data, retransmission, air interface ability estimate, etc.

3. Temporary statistic of scheduling algorithm: waiting time, average C/I, etc.

Output:

Transmit power for which users, power, channelization code, data attributes





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Max C/I Scheduling AlgorithmMax C/I Scheduling Algorithm

Features:1) Allocates channel to the user with max C/I in one TTI.

2) Provides the highest cell throughout, because channel is allocated to the user in the best radio condition .

3) It is not fair for the users located in areas of poor coverage. By max C/I algorithm, the system hardly allocate channel for users under pool signal condition.





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RR Scheduling Algorithm (RR - Round Robin)RR Scheduling Algorithm (RR - Round Robin)

Features:1) Every user has the same chance to occupy the channel and power.

2) It is very fair for every user, but it is not good to get a best cell throughput.

Note: User allocated resource





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PF Scheduling AlgorithmPF Scheduling Algorithm

Features:

1) A good balance scheme, whose fairness and resource allocation efficiency is between RR and max C/I scheduling algorithm.

2) Probability of serving all users is the same, although different users have different average channel quality.

3) This scheme accounts for balance between system throughout and fairness.

Priority for UE = R/r:

R: required data rate of UE (calculated TB size per 2ms based on CQI)

r: amount of effective data (not including data retransmitted ) transmitted by transport layer for this UE during the past 1.6s

The bigger the R/r, the higher the priority (more chance to get resource).

(PF- Proportional Fair)





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Adaptive Modulation and Coding (AMC)Adaptive Modulation and Coding (AMC)

AMC is based on channel quality Adjust data rate

Good channel condition – higher rate

Poor channel condition – lower rate

Adjust code rate Good channel condition – higher rate (e.g. 3/4 code)

Poor channel condition – lower rate (e.g. 2/4 code)

Adjust modulation scheme Good channel condition – 16QAM

Poor channel condition – QPSK

Channel Quality Feedback (CQI) UE measures channel quality (SNR) and reports to

Node B every 2ms or longer time.

Node-B chooses modulation scheme, Transport

Block size and data rate based on CQI.

AMC is based on channel quality Adjust data rate

Good channel condition – higher rate

Poor channel condition – lower rate

Adjust code rate Good channel condition – higher rate (e.g. 3/4 code)

Poor channel condition – lower rate (e.g. 2/4 code)

Adjust modulation scheme Good channel condition – 16QAM

Poor channel condition – QPSK

Channel Quality Feedback (CQI) UE measures channel quality (SNR) and reports to

Node B every 2ms or longer time.

Node-B chooses modulation scheme, Transport

Block size and data rate based on CQI.

Throughput ~ SIR RelationshipThroughput ~ SIR Relationship

AMC could improve radio bandwidth and fit for high speed radio transmission.





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HSDPA Modulation QPSK 16QAM

Modulation SchemeModulation Scheme





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CQI Mapping Table (Category 10)CQI value

Transport Block Size

Number of HS-PDSCH Modulation Reference power adjustment NIR XRV

0 N/A Out of range

1 137 1 QPSK 0

28800 0

2 173 1 QPSK 0

3 233 1 QPSK 0

4 317 1 QPSK 0

5 377 1 QPSK 0

6 461 1 QPSK 0

7 650 2 QPSK 0

… … … … …

12 1742 3 QPSK 0

13 2279 4 QPSK 0

14 2583 4 QPSK 0

15 3319 5 QPSK 0

16 3565 5 16-QAM 0

... ... ... … …

21 6554 5 16-QAM 0

22 7168 5 16-QAM 0

23 9719 7 16-QAM 0

24 11418 8 16-QAM 0

25 14411 10 16-QAM 0

26 17237 12 16-QAM 0

… … … … 0

30 25558 15 16-QAM 0

AMC and modulation scheme recommend in protocolNode-B chooses modulation scheme, transport block size and data rate based on CQI.





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Link Emulation- AMC

AMC AMC PerformancePerformance

AMC changes transmission

parameters depending on channel

condition and optimize data rate. AMC performance is affected

by channel quality error and

feedback delay in fading channel. For low data rate, AMC has

better performance than fixed MCS. For high data rate, AMC has

worse performance than fixed MCS.

AMC gai n

0

100

200

300

400

500

600

- 12 - 11 - 10 - 9 - 8 - 7 - 6 - 5 - 4 - 3

HS- DSCH Ec/ N0(dB)

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TU5(Fi xed MCS) TU5(AMC)







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AMC Processing Flow

UE measure CPICH strength UE reports the signal quality by CQI (channel quality indicator) Node B may filter and rectify CQI report to obtain actual CQI Determine the channel number, transmit power and modulation

scheme, etc, based on CQI, transmit data volume, available power and code.





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Hybrid Automatic Repeat Request (HARQ)Hybrid Automatic Repeat Request (HARQ)

Tranditional ARQ–decode received transport block

–detect if there is CRC error in decoded transport bolck

–If there is CRC error

•discard error block

•Request retransmission

Tranditional ARQ–decode received transport block

–detect if there is CRC error in decoded transport bolck


•discard error block


Hybrid ARQ–decode received transport block

–Detect if there is CRC error in decoded transport bolck


•Store error block(no discard)


•Combine the currently received retranmission with the previous failed decodes.

Hybrid ARQ–decode received transport block

–Detect if there is CRC error in decoded transport bolck


•Store error block(no discard)


•Combine the currently received retranmission with the previous failed decodes.

Soft Combine

Increment redundancy

HARQ helps minimize retransmission time and increase cell throughout.

Combined HARQ

Block1

Block1

Block1?

Block1

Block1

Block2





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HARQ Concept

HARQ is a technique that transmitter sends new set of check bits if the previous transmission failed (NACK) while receiver buffers the failed decodes for soft combining with future retransmissions.

The RV parameter indicates different code bit transmit in IR buffer. Different RV parameter configuration supports:

CC (Chase Combining): retransmit the same coded data

PIR (Partial Incremental Redundancy): transmit systematic bits first

FIR (Full Incremental Redundancy): transmit parity bits first





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HARQ Gain

One retransmission gain for different retransmission scheme

Code Rate 1/3 1/2 2/3 3/4

CC Gain (dB) 3.0 3.0 3.0 3.0

PIR Gain (dB) 3.1 3.3 3.6 6.5

FIR Gain (dB) 3.1 3.5 4.3 8.4

FIR scheme will transmit the check bits first, it has effective average coded bits after retransmission. Especially for high code rate, the HARQ gain is very evidence.





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Link Emulation- HARQ

HARQ( Hybrid ARQ) Performance

HARQ may reduce effect by channel measure error and feedback delay, and provide AMC performance gain.

Higher speed, higher HARQ gain.

HARQ Gai n over AMC

0

100

200

300

400

500

600

- 12. 5 - 11. 5 - 10. 5 - 9. 5 - 8. 5 - 7. 5 - 6. 5 - 5. 5 - 4. 5 - 3. 5

HS-DSCH Ec/ N0(dB)

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TU5(AMC+HARQ) TU5(AMC)







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Contents


Section 2 Key Techniques

Section 3 Physical Channel





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HSDPA Relevant Physical Channel Three new HSDPA Physical Channel

For each HS-DPCCH, SF=256

Each H has one HS-DPCCH.

For each HS-SCCH, SF=128

Each cell is assigned up to 4 HS-SCCH (limited by UE capability)

For each HS-PDSCH, SF=16





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HSDPA Channel Mapping





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Associated Channel - DPCH

There is another dedicated physical channel named DPCH for each HSDPA user. DPCH is also called associated channel in HSDPA. It is used for signaling transport and power control.

Normally DPCH doesn’t carry service data, only sometimes carry real time services such as AMR (the user setup multiple RAB: CS+PS).

Node B

UE

HS-PDSCH HS-SCCH DPCH HS-DPCCH

“Associated”? Or “Concomitant”?





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HSDPA Physical Channel (HS-SCCH)HS-SCCH and HS-PDSCH

are downlink shared channel shared by all users. How can users

know when and on which channel my data is

transported?

HS-SCCH and HS-PDSCH are downlink shared channel shared by all users. How can users

know when and on which channel my data is

transported?

HS-SCCH is like soldiers holding flags at the first row of queue. UE keeps on monitoring the HS-SCCH channels to identify any HS-PDSCH subframes addressed to it on the sets of HS-PDSCH channels. Upon receiving an HS-PDSCH subframe for the UE, the UE physical layer will demodulates the subframe, otherwise do nothing.

HS-SCCH is like soldiers holding flags at the first row of queue. UE keeps on monitoring the HS-SCCH channels to identify any HS-PDSCH subframes addressed to it on the sets of HS-PDSCH channels. Upon receiving an HS-PDSCH subframe for the UE, the UE physical layer will demodulates the subframe, otherwise do nothing.





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Physical Channel Slot Format (HS-SCCH) HS-SCCH Slot Format Features

3 slots in one TTI (2ms) SF=128, QPSK modulation Maps user’s seven data attributes, including Xue, Xccs, Xms, Xrv, Xtbs, Xhap and Xnd; UE demodulates HS-SCCH and find out the received data addressed to the UE. Then

UE demodulates the HS-PDSCH. In theory, one cell can configure up to 15 HS-SCCH. But now commercial UE can only

monitor up to 4 HS-SCCH channels simultaneously. So one cell only configure up to 4 HS-SCCH channels.

Slot #0 Slot#1 Slot #2

T slot = 2560 chips, 40 bits

DataN data 1 bits

HS-SCCH subframe: T = 2 ms





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Physical Channel Slot Format (HS-PDSCH)

Slot #0 Slot#1 Slot #2

T slot = 2560 chips, M*10*2 k bits (k=4)

Data N data 1 bits

1 subframe: T f = 2 ms

HS-PDSCH Slot Format Attributes:3 slots in one TTI (2ms)

Fixed spreading factor SF16

QPSK or 16QAM modulation

Only carry user data

UE may be assigned multi channelization codes to support multi-code transport depending on UE capability.





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Physical Channel Slot Format (HS-DPCCH) Uplink HS-DPCCH

TTI 2ms (3 slots), SF 256, Fixed rate of 15Kbps,carry 2 types of HSDPA uplink physical layer signaling: ACK/NACK and CQI.

ACK and NACK notifies the NodeB if UE has received correct downlink data or not. The field defines like this:1-Nack, 0-Ack

CQI is a metric that reflects physical channel quality indicator based on CPICH, and reported by period ranging from 0, 2ms…. to 160ms (0 means no transmission). Usually the period is 2ms (one TTI).

ACK/NAK and CQI having different function may be controlled independently by different parameters .

ACK/NACK/CQI could be configured to repeat up to 4 times to improve TSTD gain.

Subframe #0 Subframe # Subframe #4

HARQ-ACK CQI

One radio frame T f = 10 ms

One HS-DPCCH subframe (2 ms)

2 T slot = 5120 chips T slot = 2560 chips





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Physical Channel Timing Start of HS-SCCH is aligned with the start of P-CCPCH, HS-PDSCH subframe

is transmitted two slots after the associated HS-SCCH subframe. UE demodulates HS-PDSCH subframe according to HS-SCCH.

HS-SCCH and PDSCH are common channels, so there are not timing between HS-SCCH/PDSCH and DPCH.

HS-SCCH

HS-PDSCH

3 slots = 2 ms

DPCH

DPCH

Radio frame with (SFN modulo 2) = 0 P-CCPCH

2 slots

3 slots = 2 ms

Slot Slot Slot Slot Slot Slot Slot Slot Slot Slot Slot Slot Slot Slot Slot

15 slots = 10 ms

Subframe #0 Subframe #1 Subframe #2 Subframe #3 Subframe #4

Radio frame with (SFN modulo 2)=1

10 ms

Subframe #0 Subframe #1 Subframe #2 Subframe #3 Subframe #4

HS-DPCCH

3 slots = 2 ms

~7.5 slots





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UE Capacity Category( for reference)





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HSDPA Physical Channel Transmit Power PHSDPA(HSDPA total transmit power) ＝ PHS-PDSCH + PHS-SCCH

The HS-PDSCH transmit power is adjusted by Node B according

to the following factors:

CQI

Amount of data to be transmitted

Available power for HS-PDSCH

Available code resource for HS-PDSCH

HS-SCCH transmit power may use:

Fixed power transmission (outdoor 5%, indoor 3% of the total power)

A fixed power offset between HS-SCCH and DL associated channel

(PDCH). HS-PDSCH transmit power is usually bigger than the PDCH

channel to keep a proper transmit power.

HS-DPCCH transmit power has a power offset based on UL DPCH.

Slot carrying HARQ-ACK/NACK or CQI may be set different power offset.





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HSDPA – Channel MappingWhen RAB is mapped onto HS-DSCH, DPCH is needed to transport UL RLC AM information and possible UL data, no matter there is UL data to transport.

The following figure describes that DL TRB is carried on HS-DSCH SRB and SRB or UL service is carried on DCH. In soft handover, there may be one or more DCH, but only one HS-DSCH.

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